Inductor



NOV. l0, 1970 G, A, YOUNG 3,539,960

INDUCTOR Filed April 21, 1969 United States Patent O U.S. Cl. 336--198 9 Claims ABSTRACT OF THE DISCLOSURE A bobbin for use in making an inductor wherein the end flanges are heat fused to the central tubular portion of the bobbin. The central tubular portion of the bobbin is formed of laminates of materials generally classified as plastics, and the outer surface of the tubular portion is coated with a material which can be heat activated, such as Teilon or polyethylene. Each end llange includes an axially extending neck portion ensleeved on the central tubular portion, and the neck portion includes a layer of heat activatable plastic adjacent the central tubular portion so that the plastic of the end flange may be heat fused to the plastic of the tubular portion.

BACKGROUND AND SUMMARY This invention relates to bobbins on which a conductor Wire may be wound to provide an inductor, such as a relay. Bobbins are generally formed by positioning an end ilange adjacent each end of a tubular coil form, and thereafter securing the end flanges to the tube. The end flanges serve to confine the wire which is subsequently wound on the tubular portion, and it is important that the ilanges be securely positioned on the tube.

In the past, the llanges have been secured to the tube in a variety of Ways, as, for example, by an adhesive, by swaging, or by flaring. At times these methods of securing the flanges have not provided the desired resistance to torquing or a sufficient seal against electrical leakage in which arcing may occur from the winding to the exterior of the bobbin through a space between the llange and the tubular portion of the bobbin.

According to the instant invention, a novel laminate is used which provides a thermoplastic film on the exterior of the tubular portion of the bobbin which may be heat fused to a layer of similar plastic which is provided on the neck portion of the end flange. The heat-fused bond provides extremely high resistance to torquing, and also improves the electrical characteristics of the bobbin by reducing electrical leakage.

The invention is described in conjunction with an illustrative embodiment in the accompanying drawing, in which- FIG. 1 is a perspective view of a completed bobbin formed according to the invention which is in the process of being wound with a conductor wire;

FIG. 2 is an enlarged fragmentary sectional view taken along the line 2-2 showing the bobbin in the process of manufacture;

FIG. 3 is an enlarged fragmentary view of a portion of FIG. 2; and

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3.

Referring now to FIG. 1, the numeral designates generally a bobbin constructed in accordance with the teachings of this invention. The bobbin is seen to include a central tubular portion 11 and end flanges 12 and 13. The end fluange 12 is seen to include a generally cylindrical neck portion 14 ensleeved on one end of a tubular portion 11 and a flange portion 15 which extends generally radially outwardly from the neck portion 14. The end flange 13 is similarly formed, and after the end flanges are secured to the tubular portion, a conductor wire 16 may be wound on the tubular portion between the end flanges.

Referring to FIG. 3, the tubular portion 11 is formed by spirally winding a series of laminated strips on a conventional arbor or mandrel (not shown). For example, a rst laminate generally designated 17 is wound on the arbor with adjacent convolutions abutting each other as at 18. The laminate 17 is formed of a lamina 19 of a high temperature resistant or high melting point plastic and a lamina 20 of heat activatable or low melting point plastic. The lamina 19 has a thickness of the order of about 0.005 inch, and the lamina 20 has a thickness of the order of about 0.005 to about 0.001 inch, the layer 17 being arranged so that the lamina 19 forms the interior surface of the tube and the lamina 20 faces outwardly.

Thereafter, a second laminate generally designated 21 is spirally wound over the first laminate with adjacent convolutions abutting each other as at 22 so that the edges of adjacent layers are overlapping rather than in line. The laminate 21 includes a central lamina 23 of the high temperature resistant plastic which is coated on both sides with laminae 24 and 25 of the heat activatable plastic. The lamina 24 is in confronting relation with the lamina 20 of the previous layer, and the lamina 25 forms the outer surface of the tubular portion 11. Again, the thickness of the lamina 23 of the order of about 0.005 inch, and the thickness of each of the laminae 24 and 25 is of the order of about 0.005 to about 0.001 inch.

After the second laminated layer 21 is wound over the first layer 17, the resulting tubular construction is subjected to sufficient heat to fuse the confronting laminae 20 and 24. Thereafter, the elongated construction may be cut to form individual coil forms 11. The dimensions of the laminates 17 and 21 provide a relatively small coil form or tubular member 11 which has particular utility for use in making miniature relays and the like. Although only a single tri-lamina layer 21 is shown, it is to be understood that in many instances a greater number of such layers may be used.

Still referring to FIG. 3, the end flange 1'2 is also seen to be of a laminated construction, having a heat activatable lamina 26 and a heat resistant lamina 27 arranged so that the lamina 26 is in confronting reltion with the outer lamina 25 of the tubular portion when the flange is ensleeved on the tubular portion. After the flange is positioned adjacent an end of the tubular portion, a suitable source of heat, such as a Calrod unit heater 28 (FIG. 2) is positioned adjacent the end flange to heat-fuse the lamina 26 of the neck portion of the end flange to the lamina 25 on the tubular portion 11. The neck portion is seen to extend axially along the tubular portion to provide a substantial bonding surface. A similar procedure is followed for securing the end flange 13, and thereafter the conductor wire 16 may be wound on the tubular portion between the end flanges as illustrated in FIG. 1 to provide the desired inductor.

The particular bobbin illustrated is round in cross section, but other configurations may be used, i.e., square, rectangular, etc., depending upon the electrical application involved.

EXAMPLES The first layer 17 was formed of a lamina 19 of Kap ton, a polyimide which has relatively high heat resistance, and a lamina 20 of Teflon (e.g. polytetrafluoroethylene) which has a lower melting point than Kapton. The layer 21 was formed of a central lamina 23 of Kapton and laminae 24 and 25 of Teflon. Similarly, the end flanges 12 and 13 were formed of a lamina 26 of Teflon and a lamina 27 of Kapton. After the layers 17 and 21 were wound, the confronting Teflon laminae 20 and 24 were heat fused, the melting point of Teflon being about 550 F. Thereafter, the end flanges 12 and 13 were ensleeved on the tubular portion, and the Teflon lamina along the neck portion of each of the end flanges was heat fused to the outer Teflon lamina 25 of the tubular portion. The resulting bobbin exhibited good electrical characteristics, and the end ilanges were securely lixed to the tubular portion.

Another bobbin was formed using Kapton and Teflon as the relatively high melting point plastic and the relatively loW melting point plastic, respectively, as previously described, but the layers 17 and 21 |were adhesively united rather than being heat fused. Thereafter, the Teflon lamina of each of the end flanges was heat sealed to the outer Tellon lamina ofthe tubular portion.

Bobbins were also formed by replacing the Kapton laminae of the tubular portion and the end flanges with laminae of Mylar, which also has good resistance to heat. These bobbins exhibited properties similar to the bobbins formed by using Kapton.

Polyimides other than Kapton and polyesters other than Mylar can be used for the relatively high heat resistant plastic, and thermoplastics other than Teflon, such as polyethylene and the like, can be Iused for the laminae which are heat fused.

Rather than using pre-laminated strips to form the layers 17 and 21, the dissimilar plastic laminae can be wound separately and united as by adhesive to form these layers. Further, I have found that instead of forming the end flanges `of a laminate, they may be formed of a single layer of the heat activatable thermoplastic material which forms the outer surface of the tubular portions.

I have described the tubular portion as being formed of laminates having confronting layers ofyTeflon or-vthe like which are heat sealed, but the tubular portion may also be formed of adhesively united layers of spirally 'wound strips of Kapton, Mylar, or other high heat resistant plastics, with only outside layer being coated with the Teflon, polyethylene, or the like, since the heat sealed bond need be provided only `between the outer surface of the tubular portion and the end ilanges End flanges of bobbins constructed in accordance with my invention are securely fastened to the tubular portion of the bobbin and exhibit extremely high resistance to torquing. Also, the neck portion'of the ilangelis sealed to the tubular portion of thebobbin around the entire periphery thereof and provides an improved electrical seal by substantially preventing arcing of current from the windings to the exterior of the bobbin between the end llanges and tubular portion.

I claim: A

1. An electrical inductor comprising a hollow tubular member and end ilangessecured to the tubular member, said tubular member including aplurality of layers of spirally wound strips, the outermost of said strips being a laminate of a rst plastic and a second plastic, the rst plastic having relativelyfhigh heat resistance and the second plastic having relatively low heat resistance, the second plastic forming the outer surface of the tubular member, the end ilanges having an axially extending neck portion ensleeved on said tubular member and an outlwardly extending flange portion, said neck portion including a layer of said second plastic adjacent said outer- .moststrip and being fused thereto, and anelectricalM conductor wound on said tubular member between said end flanges.

2. The inductor of claim 1 in which said rst plastic is selected from the class consisting of polyimides and polyesters.

3. The inductor of claim 1 in which the outermost layer of said tubular member is a laminate of polytetrailuorethylene and polyimide said polytetrailuorcthylene forming the outer surface of the `tubular member and hav- .ing a thickness of the order of about 0.0005 to about 0.001 inch, said polyimide having a thickness' of the order of about 0.0005 inch.

4. A bobbin for use in an velectrical inductor comprising a hollow tubular member and an end flange secured to the tubular member, said tubular member including a plurality of layers of spirally wound strips, the outermost of said strips being a laminate of a thermoplastic and a polyimide, the thermoplastic forming the outer surface of the tubular member, the end flange having an axially extending neck portion ensleeved on said tubular member and an outwardly extending flange portion, said neck portion including a layer of thermoplastic adjacent said outermost strip and being fused thereto.

v5. The bobbin of claim 4 in which the thermoplastic of the .outermost strip and of the neck portion is polytetralluoroethylene.

6. The bobbin of claim 4 in which-the outermost layer of said tubular member is a laminate of polytetrafluoroethylene and polyimide said polytetrafluoroethylene forming the outer surface of the tubular member and having a thickness of the order of about 0.0005 to about 0.001 inch, said polyimide having'a thickness of the order of about 0.005 inch.

7. A bobbin comprising ahollow tubular member and an end flange secured to the tubular member, said tubular member including at least two`layers of spirally Wound strips, the outermost of said strips being a laminate of polytetralluoroethylene, polyimide and polytetrailuoroethylene, the next-to-outermost layer being a laminate including a lamina of polytetralluoroethylene arranged 1n confronting relation with the outermost vvlayer and heatfused thereto, the end flange having a generally cylindrical neck portion ensleeved on theend of said tubular member and a generally radially outwardly-extending flange portion, said neck portion including a layer of polytetrailuoroethylene arranged in confronting relation with said outermost layer and fused thereto.

8. The bobbin of claim 7 in which the end flange includes a layer of polyimide laminated to said polytetralluoroethylene layer.

9. The bobbin of claim 7 in which the thickness of said polytetralluoroethylene ylaminae is of the order of about 0.0005 to about 0.001 inch and the thickness of said polyimide is of the order of about 0.005 inch.

References Cited Du Pont KaptonlolyimideV Film, brochure of Du Pont Co. release date June 1967.

`ELLIOT A. GOLDB'ERG, Primary Examiner Us. c1. XR.

P01050 UNITED STATES PATENT OFFICE "s CERTIFICATE 0F CORRECTION Patent No. 3,539,960 Dated November l0, 970

Inventor(s) George A. Young It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In claim 3, last line, "0.0005" should be --o.oo5.

SIGNED ma SELED MR2 197! (SEAL) Auen:

EdwardlLFletcharJr. mm E, C. a J3 Officer @omissioner of Patent 

